A New Scientist analysis based on research papers from this year indicates that US research on hESCs leaves others trailing&colon; 45 per cent of 204 papers mentioning hESCs had at least one US-based author; UK scientists were a distant second, with 17 per cent (for full details, see bit.ly/r7N3zm). On top of that, the first trials of hESC-based treatments are taking place in the US.

It is also worth noting that the heart treatment and windpipe implant do not use hESCs but adult mesenchymal stem cells, which were not subject to Bush’s restrictions. Our analysis shows that the US also leads in research papers in this field – although not by so much.

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Yet the US does seem to lag in one key respect. Our search of the ClinicalTrials.gov database for a random sample of 30 clinical trials using these adult stem cells yielded seven in China, six in South Korea, and just three in the US. Why? Again, don’t blame Bush. The low number reflects the prudence of the US Food and Drug Administration, which approves trials. While the agency is often criticised by patient-advocates for its conservative attitude, two words justify its caution&colon; Jesse Gelsinger.

The 18-year-old died in 1999 after an experimental therapy. If a similar tragedy were to befall a stem cell trial, it could stymie the field, as Gelsinger’s death did to gene therapy. The FDA is wise to be cautious.

Bush’s restrictions may not have had the expected effect, but uncertainty still prevails&colon; a current lawsuit could yet stall federal funding to hESCs. Nevertheless, those who would restrict the research must now accept that progress is unstoppable.

Those who would restrict stem cell science must accept that progress is now unstoppable